Outdoor Wiring


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Old 03-20-20, 06:40 AM
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Outdoor Wiring

Can you bury THW wire in rigid PVC conduit to a depth of only 12" if GFCI protected? I was told by a licensed Electrician that this is acceptable but I seem to keep reading 18" depth is required. The line is served by a 40 Amp breaker. Can you clarify? Thanks
 
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Old 03-20-20, 07:58 AM
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You confusing your terms. Rigid and PVC are two different types of conduit. Rigid is steel pipes that thread together. There is no rigid PVC.
 
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Old 03-20-20, 08:01 AM
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Ok thanks for that clarification. So it was buried in PVC not rigid steel.
 
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Old 03-20-20, 09:30 AM
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Any PVC conduit needs to be buried 18" deep.
Heavy wall metal conduit doesn't need to be as deep.
 
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Old 03-20-20, 08:15 PM
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I'm seeing some conflicting information suggesting that GFCI protection lessens the depth to only 12". Can you clarify?
 
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Old 03-21-20, 07:05 AM
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Yes. If the wires/circuit are GFCI protected before it enters the ground, and is 20 amps or less, and is 120 volts or less, you are only required to bury it 12" deep in most locations. (Table 300.5 2017 NEC)

There is no rigid PVC.
Article 352 Rigid Polyvinyl Chloride Conduit: Type PVC (2017 NEC)

Note: Rigid metal or Intermediate metal conduit is only required to be buried 6" in most locations.
 

Last edited by Tolyn Ironhand; 03-21-20 at 10:36 AM. Reason: added additional info
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Old 03-21-20, 08:24 AM
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Thanks for clarifying that. So not to sound dense - so if the circuit was 40 Amps and GFCI protected before entering the ground it would need to go 18" down not 12"? Did code years ago require less burial depth? I live in a very old house and I see PVC run above ground...

Why does the Amperage of the circuit affect the burial depth?
 
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Old 03-21-20, 09:29 AM
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If it was a long time ago it may have been before the code established a burying depth.
A code established burying depth is typically only followed when an inspection is to be made.
Many homeowners running their own lines just bury the conduit/wire to whatever depth is easiest.

20A or less...... reread Tolyns post #6.
 
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Old 03-21-20, 10:35 AM
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so if the circuit was 40 Amps and GFCI protected before entering the ground it would need to go 18" down not 12"?
Correct. It would need to be buried 18" down. You could use Rigid or Intermediate metal conduit and only put it 6" down regardless of the fuse or breaker rating.

Did code years ago require less burial depth?
Perhaps in the 1930's

Why does the Amperage of the circuit affect the burial depth?
It's all about safety. A 40 amp circuit has a lot more fault current available so if somebody hit it (which often happens) there would be a bigger boom then on a 20 amp circuit. I should have also mentioned that the circuit is also required to be 120 volts or less. I will edit my previous post.
 
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Old 03-21-20, 01:27 PM
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Thanks guys for all the responses - much appreciated. So I have something of a dilemma. I had an outdoor line run recently by a licensed, very reputable electrical company. They ran a 40 Amp circuit to an outdoor structure about 100 feet away. To say it was a bear is an understatement. I know it is GFCI protected - not sure but think 120 volts but they only buried it 12". Don't really expect to need to do any work in the area that was trenched. Sprinkler system in place from long ago. No gas lines, sewer/drain lines, etc mostly along a tree line. To dig it up and retrench would be a project. Don't really expect any inspections. There are many things about my house that are not code since it was built 100 years ago - in fact there are 120 volt landscape lights probably installed 30ish years ago where the PVC was run above ground in places & where buried is not 18" down for sure.

Any suggestions?
1. Just leave it as is since realistically will probably never be an issue
2. "Cover it" somehow - shrubs/bushes? Stones?
3. Get it retrenched?
 
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Old 03-21-20, 01:42 PM
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Why did they say it was a bear ? Was it all rock ?
If it's in now..... leave it.

Mark it well so that you know where it is.
It's technically not to code but it doesn't mean it's unsafe.
 
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Old 03-21-20, 01:48 PM
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I was there while they did it - old house, stone, plaster & lathe,etc - nothing was straight forward, etc.(Rarely is in my experience) The trenching part per se was not a bear but the rest was..

I will take your advice and just leave it even though it bothers the part of me that wants things done the right way.

Any recommendations for marking it? Thanks again
 
 

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